The present invention relates to a magnetic tape cassette, and particularly to a method for image-transfer molding the half portions of the casing body of a magnetic tape cassette.
In a magnetic tape cassette, hubs on which a magnetic tape is wound are supported in a casing body composed of upper and lower half portions, which are usually manufactured by the injection molding of a plastic. After the injection molding process, paper or the like on which is printed a prescribed design is adhered to the outside surface of each of the upper and the lower portions, or the design is directly printed on the outside surface. Thus, the manufacture of each of the upper and the lower half portions requires separate steps of injection molding and attachment of the paper or the like or printing of the design. For this reason, the manufacturing process is generally complicated.
A method for image-transfer injection molding in which a prescribed design is printed on the outside surface of each of the upper and lower half portions of the casing body of a magnetic tape cassette at the same time as the injection molding of the half portion has been developed, as disclosed in the Japanese Unexamined Published Utility Model Applications Nos. 113281/88 and 118782/88. Such a method will be described with reference to FIGS. 5 and 6.
For the injection molding process, two dies 1 and 2 are set so that the recesses 3 and 4 thereof constitute a cavity whose form corresponds to that of the upper or lower half portion, and a molten plastic or the like is injected into the cavity through a runner 1b. For image transfer, an image transfer film 20 having a prescribed design in the form of an ink layer is pinched between the dies 1 and 2 so that the film is pushed onto the inside surface of the recess 4 of the die 2 when the molten plastic or the like is injected into the cavity through the runner 1b. At the time of injection, the molten plastic comes into contact with the adhesive layer 18 of the image transfer film 20, which is composed of a base film 6, a peeling layer 7, a protective layer 8, the ink layer 9 and the adhesive layer, as shown in FIG. 7, so that the protective layer and the ink layer are joined to the surface of the injected material by the adhesive layer. After the upper or lower half portion solidifies and is extracted from the dies 1 and 2, the base film 6 can be easily peeled off the upper or lower half portion because of the presence of the peeling layer 7 so that the ink layer 9 coated with the protective layer 8 is left on the outside surface of the half portion. The design of the ink layer 9 is thus transferred to the outside surface of the half portion. For the injection molding process, a pair of nearly cylindrical pins 35 and 36 are fitted in the dies 1 and 2 to provide the half portion of the cassette casing body with a hole such as a reference hole, a capstan hole and a screw hole. The pins 35 and 36 project into the cavity and have their tips in contact with each other to form the hole which extends in the direction of thickness of the half portion.
However, when the image transfer film 20 is pinched between the dies 1 and 2 as shown in FIG. 5, the film is also pinched between the tips of the pins 35 and 36. For this reason, when the base film 6 is peeled off the half portion after the latter has been removed from the dies 1 and 2, an image transfer layer 12, which is composed of the protective layer 8, the ink layer 9 and the adhesive layer 18, and which belongs to part of the image transfer film 20 and is pinched between the pins 35 and 36, is left in the hole as an unnecessary film coupled to the image transfer layer of the other part of the image transfer film stuck to the outside surface of the half portion. Even if the image transfer layer 12 left as an unnecessary film is pierced together with the base film 6 by a sharp-edged pin, as disclosed in Japanese Unexamined Published Utility Model Application No. 113281/88, it is difficult to completely remove the image transfer layer along the inside surface of the hole. Thus, the method of image-transfer injection molding requires a step of completely removing the image transfer layer 12 following injection molding. This, too, is a problem.